Study of the formation of the photosynthetic apparatus (chromatophore) of Athiorhodaceae will be undertaken as a model for cellular differentiation: A. Regulation and transmission of genetic information for chromatophore formation by plasmid genes will be investigated by: (1) analyzing and isolating plasmid DNA's from various Athiorhodaceae by analytical and preparative ultracentrifugation and DNA-DNA hybridization; (2) studying the spontaneous and induced loss of genetic information for chromatophore formation; (3) determining if genetic information for photosynthesis can be transmitted, intra- or interspecifically, and (4) determining if mRNA specific to the photosynthetic state is homologous to plasmid DNA's by RNA-DNA hybridization. B. Alterations in specificity of DNA-dependent RNA polymerasa in chromatophore development will be examined by: (1) isolating mutants with altered RNA polymerases using the antibiotics rifampicin and streptolydigin, and analyzing the ability of these mutants to carry out cellular differentiation; and (2) extracting and purifying RNA polymerases from dark-grown and photosynthetic cells, and comparing template specificity and physiocochemical characteristics. C. The mechanism of O2 repression of the chromatophore will be studied by isolation and analysis of mutants with an altered response to O2. D. The regulatory mechanism which controls chromatophore formation will be examined by analysis of mutants with conditional regulatory defects.